Method and apparatus for signaling skip mode flag

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry. In some embodiments, processing circuitry decodes, prediction information for a block in an I slice from a coded video bitstream, and determines, whether an intra block copy (IBC) mode is possible for the block in the I slice. In response to a slice type parameter indicating I slice and at least a width or height of the block being greater than 64, the processing circuitry sets a current mode type parameter to MODE_TYPE_INTRA. Further, in an embodiment, the processing circuitry decodes a flag that indicates whether a skip mode is applied on the block from the coded video bitstream. Then, the processing circuitry reconstructs the block at least partially based on the flag.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/959,621, “METHODS FOR SIGNALING OF SKIPMODE FLAG” filed on Jan. 10, 2020, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction and intra-picture prediction. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 shows a schematic (201) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 3, a current block (301) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (302 through 306, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. In someembodiments, processing circuitry decodes, prediction information for ablock in an I slice from a coded video bitstream, and determines,whether an intra block copy (IBC) mode is possible for the block in theI slice based on the prediction information and a size restriction ofthe IBC mode. Further, in an embodiment, the processing circuitrydecodes, in response to the IBC mode being possible for the block in theI slice, a flag that indicates whether a skip mode is applied on theblock from the coded video bitstream. Then, the processing circuitryreconstructs the block at least partially based on the flag.

Further, in some examples, the processing circuitry infers the flag inresponse to the IBC mode being impossible for the block in the I slice.

In some embodiments, the processing circuitry determines that the IBCmode is impossible for the block in the I slice in response to a size ofthe block in the I slice being larger than a threshold. In anembodiment, the processing circuitry determines that the IBC mode isimpossible for the block in the I slice in response to at least one of awidth of the block and a height of the block being larger than thethreshold. In some examples, the processing circuitry determines anexistence of the flag in the coded video bitstream based on an addedcondition that compares the size of the block with the threshold. Theadded condition excludes the existence of the flag in response to thesize of the block in the I slice being larger than the threshold.

In some examples, the processing circuitry determines an existence ofthe flag in the coded video bitstream based on an existing conditionthat is modified to base on a comparison of the size and the threshold.In an example, the existing condition determines whether the block is aninter coded block. In another example, the existing condition determineswhether the IBC mode is enabled.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 2 is an illustration of exemplary intra prediction directions.

FIG. 3 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of acommunication system (500) in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 7 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 8 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 9 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 10 shows an example of intra block copy according to an embodimentof the disclosure.

FIG. 11 shows an exemplary syntax table for signaling prediction mode atthe coding unit level.

FIGS. 12A-12E show an exemplary syntax table of coding tree unit level.

FIG. 13 shows an exemplary syntax table at coding unit level accordingto some embodiments of the disclosure.

FIG. 14 shows an exemplary syntax table at coding tree level accordingto some embodiments of the disclosure.

FIG. 15 shows a flow chart outlining a process example according to someembodiments of the disclosure.

FIG. 16 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 4 illustrates a simplified block diagram of a communication system(400) according to an embodiment of the present disclosure. Thecommunication system (400) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (450). Forexample, the communication system (400) includes a first pair ofterminal devices (410) and (420) interconnected via the network (450).In the FIG. 4 example, the first pair of terminal devices (410) and(420) performs unidirectional transmission of data. For example, theterminal device (410) may code video data (e.g., a stream of videopictures that are captured by the terminal device (410)) fortransmission to the other terminal device (420) via the network (450).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (420) may receive the codedvideo data from the network (450), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (400) includes a secondpair of terminal devices (430) and (440) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (430) and (440)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (430) and (440) via the network (450). Eachterminal device of the terminal devices (430) and (440) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (430) and (440), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 4 example, the terminal devices (410), (420), (430) and(440) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (450) represents any number ofnetworks that convey coded video data among the terminal devices (410),(420), (430) and (440), including for example wireline (wired) and/orwireless communication networks. The communication network (450) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(450) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 5 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (513), that caninclude a video source (501), for example a digital camera, creating forexample a stream of video pictures (502) that are uncompressed. In anexample, the stream of video pictures (502) includes samples that aretaken by the digital camera. The stream of video pictures (502),depicted as a bold line to emphasize a high data volume when compared toencoded video data (504) (or coded video bitstreams), can be processedby an electronic device (520) that includes a video encoder (503)coupled to the video source (501). The video encoder (503) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (504) (or encoded video bitstream (504)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (502), can be stored on a streamingserver (505) for future use. One or more streaming client subsystems,such as client subsystems (506) and (508) in FIG. 5 can access thestreaming server (505) to retrieve copies (507) and (509) of the encodedvideo data (504). A client subsystem (506) can include a video decoder(510), for example, in an electronic device (530). The video decoder(510) decodes the incoming copy (507) of the encoded video data andcreates an outgoing stream of video pictures (511) that can be renderedon a display (512) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (504),(507), and (509) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (520) and (530) can includeother components (not shown). For example, the electronic device (520)can include a video decoder (not shown) and the electronic device (530)can include a video encoder (not shown) as well.

FIG. 6 shows a block diagram of a video decoder (610) according to anembodiment of the present disclosure. The video decoder (610) can beincluded in an electronic device (630). The electronic device (630) caninclude a receiver (631) (e.g., receiving circuitry). The video decoder(610) can be used in the place of the video decoder (510) in the FIG. 5example.

The receiver (631) may receive one or more coded video sequences to bedecoded by the video decoder (610); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (601), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (631) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (631) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (615) may be coupled inbetween the receiver (631) and an entropy decoder/parser (620) (“parser(620)” henceforth). In certain applications, the buffer memory (615) ispart of the video decoder (610). In others, it can be outside of thevideo decoder (610) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (610), forexample to combat network jitter, and in addition another buffer memory(615) inside the video decoder (610), for example to handle playouttiming. When the receiver (631) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (615) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (615) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (610).

The video decoder (610) may include the parser (620) to reconstructsymbols (621) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (610),and potentially information to control a rendering device such as arender device (612) (e.g., a display screen) that is not an integralpart of the electronic device (630) but can be coupled to the electronicdevice (630), as was shown in FIG. 6. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (620) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (620) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (620) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (620) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (615), so as tocreate symbols (621).

Reconstruction of the symbols (621) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (620). The flow of such subgroup control information between theparser (620) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (610)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (651). Thescaler/inverse transform unit (651) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (621) from the parser (620). The scaler/inversetransform unit (651) can output blocks comprising sample values, thatcan be input into aggregator (655).

In some cases, the output samples of the scaler/inverse transform (651)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (652). In some cases, the intra pictureprediction unit (652) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (658). The currentpicture buffer (658) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(655), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (652) has generated to the outputsample information as provided by the scaler/inverse transform unit(651).

In other cases, the output samples of the scaler/inverse transform unit(651) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (653) canaccess reference picture memory (657) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (621) pertaining to the block, these samples can beadded by the aggregator (655) to the output of the scaler/inversetransform unit (651) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (657) from where themotion compensation prediction unit (653) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (653) in the form of symbols (621) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (657) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (655) can be subject to variousloop filtering techniques in the loop filter unit (656). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (656) as symbols (621) from the parser (620), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (656) can be a sample stream that canbe output to the render device (612) as well as stored in the referencepicture memory (657) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (620)), the current picture buffer (658) can becomea part of the reference picture memory (657), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (610) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (631) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (610) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 7 shows a block diagram of a video encoder (703) according to anembodiment of the present disclosure. The video encoder (703) isincluded in an electronic device (720). The electronic device (720)includes a transmitter (740) (e.g., transmitting circuitry). The videoencoder (703) can be used in the place of the video encoder (503) in theFIG. 5 example.

The video encoder (703) may receive video samples from a video source(701) (that is not part of the electronic device (720) in the FIG. 7example) that may capture video image(s) to be coded by the videoencoder (703). In another example, the video source (701) is a part ofthe electronic device (720).

The video source (701) may provide the source video sequence to be codedby the video encoder (703) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (701) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (701) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (703) may code andcompress the pictures of the source video sequence into a coded videosequence (743) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (750). In some embodiments, the controller(750) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (750) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (750) can be configured to have other suitablefunctions that pertain to the video encoder (703) optimized for acertain system design.

In some embodiments, the video encoder (703) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (730) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (733)embedded in the video encoder (703). The decoder (733) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (734). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (734) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (733) can be the same as of a“remote” decoder, such as the video decoder (610), which has alreadybeen described in detail above in conjunction with FIG. 6. Brieflyreferring also to FIG. 6, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (745) and the parser (620) can be lossless, the entropy decodingparts of the video decoder (610), including the buffer memory (615), andparser (620) may not be fully implemented in the local decoder (733).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (730) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (732) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (733) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (730). Operations of the coding engine (732) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 7), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (733) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (734). In this manner, the video encoder(703) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (735) may perform prediction searches for the codingengine (732). That is, for a new picture to be coded, the predictor(735) may search the reference picture memory (734) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(735) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (735), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (734).

The controller (750) may manage coding operations of the source coder(730), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (745). The entropy coder (745)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (740) may buffer the coded video sequence(s) as createdby the entropy coder (745) to prepare for transmission via acommunication channel (760), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(740) may merge coded video data from the video coder (703) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (750) may manage operation of the video encoder (703).During coding, the controller (750) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (703) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (703) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (740) may transmit additional datawith the encoded video. The source coder (730) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 8 shows a diagram of a video encoder (803) according to anotherembodiment of the disclosure. The video encoder (803) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (803) is used in theplace of the video encoder (503) in the FIG. 5 example.

In an HEVC example, the video encoder (803) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (803) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (803) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(803) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (803) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 8 example, the video encoder (803) includes the interencoder (830), an intra encoder (822), a residue calculator (823), aswitch (826), a residue encoder (824), a general controller (821), andan entropy encoder (825) coupled together as shown in FIG. 8.

The inter encoder (830) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (822) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (822) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (821) is configured to determine general controldata and control other components of the video encoder (803) based onthe general control data. In an example, the general controller (821)determines the mode of the block, and provides a control signal to theswitch (826) based on the mode. For example, when the mode is the intramode, the general controller (821) controls the switch (826) to selectthe intra mode result for use by the residue calculator (823), andcontrols the entropy encoder (825) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(821) controls the switch (826) to select the inter prediction resultfor use by the residue calculator (823), and controls the entropyencoder (825) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (823) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (822) or the inter encoder (830). Theresidue encoder (824) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (824) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (803) also includes a residuedecoder (828). The residue decoder (828) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (822) and theinter encoder (830). For example, the inter encoder (830) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (822) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (825) is configured to format the bitstream toinclude the encoded block. The entropy encoder (825) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (825) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 9 shows a diagram of a video decoder (910) according to anotherembodiment of the disclosure. The video decoder (910) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (910) is used in the place of the videodecoder (510) in the FIG. 5 example.

In the FIG. 9 example, the video decoder (910) includes an entropydecoder (971), an inter decoder (980), a residue decoder (973), areconstruction module (974), and an intra decoder (972) coupled togetheras shown in FIG. 9.

The entropy decoder (971) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (972) or the inter decoder (980), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (980); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (972). The residual information can be subject to inversequantization and is provided to the residue decoder (973).

The inter decoder (980) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (972) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (973) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (973) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (971) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (974) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (973) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (503), (703), and (803), and thevideo decoders (510), (610), and (910) can be implemented using anysuitable technique. In an embodiment, the video encoders (503), (703),and (803), and the video decoders (510), (610), and (910) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (503), (703), and (703), and the videodecoders (510), (610), and (910) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide signaling techniques for skip modeflag.

Block based compensation can be used for inter prediction and intraprediction. For the inter prediction, block based compensation from adifferent picture is known as motion compensation. For intra prediction,block based compensation can also be done from a previouslyreconstructed area within the same picture. The block based compensationfrom reconstructed area within the same picture is referred to as intrapicture block compensation, current picture referencing (CPR) or intrablock copy (IBC). A displacement vector that indicates the offsetbetween the current block and the reference block in the same picture isreferred to as a block vector (or BV for short). Different from a motionvector in motion compensation, which can be at any value (positive ornegative, at either x or y direction), a block vector has a fewconstraints to ensure that the reference block is available and alreadyreconstructed. Also, in some examples, for parallel processingconsideration, some reference area that is tile boundary or wavefrontladder shape boundary is excluded.

The coding of a block vector could be either explicit or implicit. Inthe explicit mode (or referred to as advanced motion vector prediction(AMVP) mode in inter coding), the difference between a block vector andits predictor is signaled; in the implicit mode, the block vector isrecovered from a predictor (referred to as block vector predictor), in asimilar way as a motion vector in merge mode. The resolution of a blockvector, in some implementations, is restricted to integer positions; inother systems, the block vector is allowed to point to fractionalpositions.

In some examples, the use of intra block copy at block level, can besignaled using a block level flag that is referred to as an IBC flag. Inan embodiment, the IBC flag is signaled when the current block is notcoded in merge mode. In other examples, the use of the intra block copyat block level is signaled by a reference index approach. The currentpicture under decoding is then treated as a reference picture. In anexample, such a reference picture is put in the last position of a listof reference pictures. This special reference picture is also managedtogether with other temporal reference pictures in a buffer, such asdecoded picture buffer (DPB).

There are also some variations for intra block copy, such as flippedintra block copy (the reference block is flipped horizontally orvertically before used to predict current block), or line based intrablock copy (each compensation unit inside an M×N coding block is an M×1or 1×N line).

FIG. 10 shows an example of intra block copy according to an embodimentof the disclosure. Current picture (1000) is under decoding. The currentpicture (1000) includes a reconstructed area (1010) (doted area) andto-be-decoded area (1020) (white area). A current block (1030) is underreconstruction by a decoder. The current block (1030) can bereconstructed from a reference block (1040) that is in the reconstructedarea (1010). The position offset between the reference block (1040) andthe current block (1030) is referred to as a block vector (1050) (or BV(1050)).

In some examples, the intra block copy is considered as a separate modeother than the intra prediction mode or the inter prediction mode, thesignaling of intra block copy can be specified at block level using acombination of flags, such as pred_mode_ibc_flag and pred_mode_flag.

In a related example, a coding block may be coded in the intraprediction mode or the inter prediction mode. In the related example, aprediction mode flag “pred_mode_flag” with 1 bit can be signaled orinferred at coding block level to differentiate the coding modes for thecurrent block. For example, if pred_mode_flag is equal to 0, MODE_INTER(inter prediction mode) is used; otherwise (pred_mode_flag is equal to1), MODE_INTRA (intra prediction mode) is used.

When intra block copy is used, the mode decision can be determined basedon both the values of pred_mode_flag and pred_mode_ibc_flag.

In some examples (e.g., a version of VVC), the maximum block size for aninter coded CU can be as large as 128×128; the maximum block size for anintra coded CU can be as large as 128×128; the maximum block size for anintra block copy coded CU can be as large as 64×64, all in luma codedsamples. When luma/chroma separate coding tree is used, the largestpossible chroma CU size in 4:2:0 color format will be 32×32.

In some examples, for blocks that are inter coded (coded using interprediction mode) or IBC coded (coded using IBC mode), motion parameterscan be predicted, for example, in a merge mode or a skip mode. In themerge mode, a video coder constructs a candidate list of motionparameters (e.g., reference pictures and motion vectors) using ascandidates motion parameters from neighboring blocks, including spatialneighboring blocks and temporal neighboring blocks. The chosen motionparameters can be signaled from a video encoder to a video decoder bytransmitting an index of the selected candidate from the candidate list.At the video decoder, once the index is decoded, the motion parametersof the corresponding block of the selected candidate can be inherited.The video encoder and the video decoder are configured to construct thesame lists based on already coded blocks. Therefore, based on the index,the video decoder can identify the motion parameters of the candidateselected by the video encoder.

In the skip mode, the motion parameters can be similarly predicted as inthe merge mode. Further, in the skip mode, no residual data is added tothe predicted block, whereas in merge mode, residual data is added tothe predicted block. The constructing of a list and transmitting of anindex to identify a candidate in the list described above with referenceto the merge mode is generally also performed in the skip mode. In someembodiments, a skip flag in the coding block level can be used toindicate whether a block is coded using skip mode or not.

FIG. 11 shows an exemplary syntax table (1100) for signaling predictionmode at the coding unit (or coding block) level. The syntax table (1100)conditionally extracts, from the coded video bitstream, three flags,cu_skip_flag, pred_mode_flag and pred_mode_ibc_flag, as shown by (1101),(1102) and (1103) in FIG. 11.

Specifically, cu_skip_flag[x0][y0] is the skip flag. The skip flagcu_skip_flag[x0][y0] equal to 1 specifies that the current coding unitis coded in the skip mode. Thus, when the current coding unit is in a P(coded by inter prediction) or B (coded by bi directional interprediction) slice, no more syntax elements except one or more of thefollowing are parsed after cu_skip_flag[x0][y0]: the IBC mode flagpred_mode_ibc_flag [x0][y0], and the merge_data( ) syntax structure.When the current coding unit is in an I slice, no more syntax elementsexcept merge_idx[x0][y0] are parsed after cu_skip_flag[x0][y0].

The skip flag cu_skip_flag[x0][y0] equal to 0 specifies that the codingunit is not in the skip mode. The array indices x0, y0 specify thelocation (x0, y0) of the top-left luma sample of the considered codingblock relative to the top-left luma sample of the picture.

When cu_skip_flag[x0][y0] is not present in the coded video bitstream,cu_skip_flag[x0][y0] can be inferred to be equal to 0.

Further, pred_mode_flag equal to 0 specifies that the current codingunit is coded in the inter prediction mode; and pred_mode_flag equal to1 specifies that the current coding unit is coded in intra predictionmode.

In some embodiments, pred_mode_flag is not present in the coded videobitstream, and pred_mode_flag can be inferred. The inference of thepred_mode_flag can be based on a variable modeType. Generally, thevariable modeType specifies whether intra prediction mode (MODE_INTRA),IBC mode (MODE_IBC), palette mode (MODE_PLT), and inter prediction modecan be used (MODE_TYPE_ALL), or whether only intra, IBC and palettecoding modes can be used (MODE_TYPE_INTRA), or whether only inter codingmodes can be used (MODE_TYPE_INTER) for coding units inside the codingtree node. For example, when the variable modeType is MODE_TYPE_ALL, allof the intra prediction mode, IBC mode, palette mode, and interprediction mode can be used; when the variable modeType isMODE_TYPE_INTRA, the intra prediction mode, IBC mode and palette modecan be used; and when the variable modeType is MODE_TYPE_INTER, onlyinter prediction mode can be used.

In some examples, the variable, modeType, is used to control thepossible allowed prediction mode types for certain small CU sizes. Atthe CTU root (where coding_tree( ) syntax is firstly called), the valueof this variable is set to be MODE_TYPE_ALL (meaning no constraints).Therefore, for a large CU, such as 128×128 128×64, 64×128, modeTypeshould be set to MODE_TYPE_ALL. When the large CU is split into smallerCUs, the variable modeType for the small CUs can be refined, such asbased on a variable treeType. In an embodiment, the coding tree schemesupports the ability for a luma component and corresponding chromacomponent(s) to have separate block tree structures. In an example, forP and B slices, luma and chroma CTBs in a CTU share a same coding treestructure (e.g., a single tree). For I slices, luma and chroma CTBs in aCTU can have separate block tree structures (e.g., dual tree), and thepartition case of the CTU using separate block tree structures isreferred to as dual tree partition. When dual tree partition is applied,a luma CTB can be partitioned into luma CUs by a luma coding treestructure (e.g., DUAL_TREE_LUMA), and chroma CTBs can be partitionedinto chroma CUs by a chroma coding tree structure (e.g.,DUAL_TREE_CHROMA). Thus, a CU in an I slice can include a coding blockof the luma component and can include coding blocks of two chromacomponents, and a CU in a P or B slice includes coding blocks of allthree color components unless the video is monochrome. In an example,the variable treeType specifies whether a single tree (SINGLE_TREE) or adual tree is used for a coding unit split from a coding tree unit; whena dual tree is used, the variable treeType specifies whether the luma(DUAL_TREE_LUMA) or chroma components (DUAL_TREE_CHROMA) are currentlyprocessed.

In some embodiments, pre_mode_flag is be inferred as follows:

-   -   If cbWidth (width of the coding unit) is equal to 4 and cbHeight        (height of the coding unit) is equal to 4, pred_mode_flag is        inferred to be equal to 1 due to the reason in some example,        inter prediction mode is not applied to 4×4 blocks;    -   otherwise, if modeType is equal to MODE_TYPE_INTRA,        pred_mode_flag is inferred to be equal to 1;    -   otherwise, if modeType is equal to MODE_TYPE_INTER,        pred_mode_flag is inferred to be equal to 0;    -   otherwise, pred_mode_flag is inferred to be equal to 1 when        decoding an I slice, and equal to 0 when decoding a P or B        slice, respectively.

The variable CuPredMode[chType][x][y] is prediction mode derived asfollows for x=x0 . . . x0+cbWidth? 1 and y=y0 . . . y0+cbHeight? 1:

-   -   If pred_mode_flag is equal to 0, CuPredMode[chType][x][y] is set        equal to MODE_INTER (inter prediction mode);    -   otherwise (pred_mode_flag is equal to 1),        CuPredMode[chType][x][y] is set equal to MODE_INTRA (intra        prediction mode).

Further, the flag pred_mode_ibc_flag equal to 1 specifies that thecurrent coding unit is coded in IBC mode. The flag pred_mode_ibc_flagequal to 0 specifies that the current coding unit is not coded in IBCmode.

In some embodiments, pred_mode_ibc_flag is not present in the codedbitstream and can be inferred. The inference of pred_mode_ibc_flag canbe based on the variable modeType and the variable treeType.

For example, the pred_mode_ibc_flag can be inferred as follows:

-   -   If cu_skip_flag[x0][y0] is equal to 1, and cbWidth is equal to        4, and cbHeight is equal to 4, pred_mode_ibc_flag is inferred to        be equal 1;    -   otherwise, if either cbWidth or cbHeight are equal to 128,        pred_mode_ibc_flag is inferred to be equal to 0;    -   otherwise, if modeType is equal to MODE_TYPE_INTER,        pred_mode_ibc_flag is inferred to be equal to 0;    -   otherwise, if treeType is equal to DUAL_TREE_CHROMA,        pred_mode_ibc_flag is inferred to be equal to 0;    -   otherwise, pred_mode_ibc_flag is inferred to be equal to the        value of sps_ibc_enabled_flag when decoding an I slice, and 0        when decoding a P or B slice, respectively.

When pred_mode_ibc_flag is equal to 1, the variableCuPredMode[chType][x][y] is set to be equal to MODE_IBC for x=x0 . . .x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1.

FIGS. 12A-12E show an exemplary syntax table (1200) at coding tree unitlevel. In the example, the input parameter modeTypeCurr is the modeTypevariable inherited from its parent node.

It is noted that the syntax and semantics in some examples, such as inthe syntax in FIG. 11, cannot correctly reflect the block sizeconstraints applied among intra/inter/IBC modes. For example, conditions(1110) in FIG. 11 is equivalent to perform a logical or (∥) of a firstcondition (!(cbWidth==4 && cbHeight==4) && (modeType!==MODE_TYPE_INTRA)) and a second condition (sps_ibc_enabled_flag). Thefirst condition checks whether the logical value of (!(cbWidth==4 &&cbHeight==4) && (modeType !==MODE_TYPE_INTRA)) is 1 or 0. The secondcondition checks whether the logical value of (sps_ibc_enabled_flag) is1 or 0. The first condition being 1 specifies that the current blockunder coding is an inter coded block. The second condition being 1specifies that IBC mode is enabled. In the FIG. 11 example, when atleast one of the first condition and the second condition is equal to 1,and the treeType is not equal to DUAL_TREE_CHROMA, the skip flag (e.g.,cu_skip_flag[x0][y0]) is presented in the coded video bitstream, and canbe decoded. However, in an example, a coding unit in an I slice can haveat least one size (width and/or height) larger than 64. Parameters ofthe coding unit can cause the first condition to be 1 and/or the secondcondition to be 1. However, the coding unit cannot be inter coded (dueto in the I slice) and cannot be IBC coded (due to the reason that atleast one size is larger than 64). Thus, the conditions (1110) cannotcorrectly reflect the block size constraints applied amongintra/inter/IBC modes.

Some aspects of the disclosure provide techniques to correctly reflectthe block size constrains applied among intra/inter/IBC modes. Thefollowing descriptions are based on the assumption that the intra blockcopy (IBC) mode is considered as a separate mode, different from intraor inter modes. The techniques can signal the skip flag (e.g.,cu_skip_flag[x0][y0]) only when the IBC mode is possible in an I slice.If only intra mode is possible, the skip flag does not need to besignaled; instead, the skip flag can be inferred to be 0.

In an embodiment, additional condition(s) can be imposed on thesignaling of skip flag such that when the CU block size suggests thatonly intra mode is possible (the block size exceed maximum IBC blocksize), the skip flag is not signaled (is not presented in the codedvideo bitstream). Instead, the skip flag can be inferred to be 0.

In an example, when a block in the I slice is larger than 64 lumasamples at either width side or height side, the block cannot be intercoded and cannot be IBC coded, and thus only intra mode (intraprediction mode) is possible for the block.

FIG. 13 shows an exemplary syntax table (1300) according to someembodiments of the disclosure. As shown by (1310) in FIG. 13, thirdcondition (!(slice_type=I && (cbWidth>64∥cbHeight>64))) is added tocombine (use logical and operator &&) with the first condition and thesecond condition. When a block in the I slice is larger than 64 lumasamples at either width side or height side, the third condition can be0. Then, the combination of the first condition, the second conditionand the third condition is equal to 0. Thus, the skip flag(cu_skip_flag[x0][y0]) is not signaled (is not presented in the codedvideo bitstream).

In another embodiment, the first condition and/or the second conditioncan be suitably modified to apply the size restrictions for IBC mode. Insome examples, the assignment of modeType is modified such that when theCU block size suggests that only intra mode is possible in I slice (theblock size exceeds maximum IBC block size), the modeType is set toMODE_TYPE_INTRA that can cause the first condition to be equal to 0. Insome embodiments, if (slice_type==I && (cbWidth>64∥cbHeight>64)), thenthe modeType is set to MODE_TYPE_INTRA.

FIG. 14 shows an exemplary syntax table (1400) at coding tree levelaccording to some embodiments of the disclosure. As shown by (1410),when a block in an I slice is larger than 64 luma samples at eitherwidth side or height side, a variable modeTypeCurr is set toMODE_TYPE_INTRA. The variable modeTypeCurr is the input parameter tocoding_unit( ) syntax as shown by the syntaxes in FIG. 14 and FIG. 13.Therefore, in the coding_unit( ) syntax table, the result of the firstcondition is 0. In another example, in the coding_unit( ) syntax, thevariable modeType is set to MODE_TYPE_INTRA before the first “if” clausewhen a block in an I slice is larger than 64 luma samples at eitherwidth side or height side. Thus, the result of the first condition is 0.

In some examples, the second conditions can be modified to apply thesize restrictions for IBC mode. For example, the second condition ismodified to be (sps_ibc_enabled_flag && cbWidth<=64 && cbHeight<=64).Thus, when a block in an I slice is larger than 64 luma samples ateither width side or height side, the result of the second condition is0.

It is noted that the embodiments in the present disclosure can be usedseparately or combined in any order.

FIG. 15 shows a flow chart outlining a process (1500) according to anembodiment of the disclosure. The process (1500) can be used in thereconstruction of a block, so to generate a prediction block for theblock under reconstruction. In various embodiments, the process (1500)are executed by processing circuitry, such as the processing circuitryin the terminal devices (410), (420), (430) and (440), the processingcircuitry that performs functions of the video encoder (503), theprocessing circuitry that performs functions of the video decoder (510),the processing circuitry that performs functions of the video decoder(610), the processing circuitry that performs functions of the videoencoder (703), and the like. In some embodiments, the process (1500) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1500). The process starts at (S1501) and proceeds to(S1510).

At (S1510), prediction information for a block in an I slice is decodedfrom a coded video bitstream.

At (S1520), whether the IBC mode is possible for the block is determinedbased on the prediction information and a size restriction of the IBCmode. In some embodiments, the IBC mode is determined to be impossiblefor the block in the I slice in response to a size of the block beinglarger than a threshold. In an embodiment, the IBC mode is determined tobe impossible for the block when at least one of a width or a height ofthe block is larger than the threshold.

In some embodiments, the possibility of the IBC mode for the block inthe I slice determines whether a flag (skip mode flag) for the block isin the coded video bitstream. In some examples, the syntax includes someexisting conditions to determine the existence of the skip mode flag. Inan embodiment, the existence of the flag in the coded video bitstream isalso determined based on an added condition that compares the size ofthe block with the threshold. The added condition excludes the existenceof the flag in response to the size of the block in the I slice beinglarger than the threshold.

In another embodiment, the existence of the flag in the coded videobitstream is determined based on an existing condition that is modifiedto compare the size of the block with the threshold. In an example, theexisting condition is the first condition that determines whether theblock is an inter coded block, and the first condition is modified tobase on a comparison of the size of the block with the threshold. Inanother example, the existing condition is the second condition thatdetermines whether the IBC mode is enabled, and the second condition ismodified to base on a comparison of the size of the block with thethreshold.

At (S1530), a flag that indicates whether a skip mode is applied on theblock is decoded from the bitstream in response to the IBC mode beingpossible for the block in the I slice in some examples. Further, in someexamples, the flag can be inferred in response to the IBC mode beingimpossible for the block in the I slice.

At (S1540), the block is reconstructed at least partially based on theflag. In an example, when the flag indicates a skip mode, the block isreconstructed based on the skip mode. Then, the process proceeds to(S1599) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 16 shows a computersystem (1600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 16 for computer system (1600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1600).

Computer system (1600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1601), mouse (1602), trackpad (1603), touchscreen (1610), data-glove (not shown), joystick (1605), microphone(1606), scanner (1607), camera (1608).

Computer system (1600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1610), data-glove (not shown), or joystick (1605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1609), headphones(not depicted)), visual output devices (such as screens (1610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1620) with CD/DVD or the like media (1621), thumb-drive (1622),removable hard drive or solid state drive (1623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1600) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1649) (such as, for example USB ports of thecomputer system (1600)); others are commonly integrated into the core ofthe computer system (1600) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1600) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1640) of thecomputer system (1600).

The core (1640) can include one or more Central Processing Units (CPU)(1641), Graphics Processing Units (GPU) (1642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1643), hardware accelerators for certain tasks (1644), and so forth.These devices, along with Read-only memory (ROM) (1645), Random-accessmemory (1646), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1647), may be connectedthrough a system bus (1648). In some computer systems, the system bus(1648) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1648),or through a peripheral bus (1649). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1641), GPUs (1642), FPGAs (1643), and accelerators (1644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1645) or RAM (1646). Transitional data can be also be stored in RAM(1646), whereas permanent data can be stored for example, in theinternal mass storage (1647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1641), GPU (1642), massstorage (1647), ROM (1645), RAM (1646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1600), and specifically the core (1640) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1640) that are of non-transitorynature, such as core-internal mass storage (1647) or ROM (1645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding, by a processor, prediction information for a blockin an I slice from a coded video bitstream; determining, by theprocessor, whether an intra block copy (IBC) mode is possible for theblock in the I slice based on the prediction information and a sizerestriction of the IBC mode; in response to a slice type parameterindicating the I slice and at least a width or height of the block beinggreater than 64, setting a current mode type parameter toMODE_TYPE_INTRA; decoding, by the processor, a flag that indicateswhether a skip mode is applied on the block from the coded videobitstream; and reconstructing, by the processor, the block at leastpartially based on the flag.
 2. The method of claim 1, furthercomprising: inferring, by the processor, the flag in response to the IBCmode being impossible for the block in the I slice.
 3. The method ofclaim 1, further comprising: determining that the IBC mode is impossiblefor the block in the I slice in response to a size of the block in the Islice being larger than a threshold.
 4. The method of claim 3, furthercomprising: determining that the IBC mode is impossible for the block inthe I slice in response to at least one of a width of the block and aheight of the block being larger than the threshold.
 5. The method ofclaim 3, further comprising: determining an existence of the flag in thecoded video bitstream based on an added condition that compares the sizeof the block with the threshold, the added condition excluding theexistence of the flag in response to the size of the block in the Islice being larger than the threshold.
 6. The method of claim 3, furthercomprising: determining an existence of the flag in the coded videobitstream based on an existing condition that is modified to compare thesize of the block with the threshold.
 7. The method of claim 6, whereinthe existing condition determines whether the block is an inter codedblock.
 8. The method of claim 6, wherein the existing conditiondetermines whether the IBC mode is enabled.
 9. An apparatus for videodecoding, comprising processing circuitry configured to: decode,prediction information for a block in an I slice from a coded videobitstream; determine, whether an intra block copy (IBC) mode is possiblefor the block in the I slice based on the prediction information and asize restriction of the IBC mode; in response to a slice type parameterindicating the I slice and at least a width or height of the currentblock being greater than 64, set a current mode type parameter toMODE_TYPE_INTRA; decode a flag that indicates whether a skip mode isapplied on the block from the coded video bitstream; and reconstruct theblock at least partially based on the flag.
 10. The apparatus of claim9, wherein the processing circuitry is configured to: infer the flag inresponse to the IBC mode being impossible for the block in the I slice.11. The apparatus of claim 9, wherein the processing circuitry isconfigured to: determine that the IBC mode is impossible for the blockin the I slice in response to a size of the block in the I slice beinglarger than a threshold.
 12. The apparatus of claim 11, wherein theprocessing circuitry is configured to: determine that the IBC mode isimpossible for the block in the I slice in response to at least one of awidth of the block and a height of the block being larger than thethreshold.
 13. The apparatus of claim 11, wherein the processingcircuitry is configured to: determine an existence of the flag in thecoded video bitstream based on an added condition that compares the sizeof the block with the threshold, the added condition excluding theexistence of the flag in response to the size of the block in the Islice being larger than the threshold.
 14. The apparatus of claim 11,wherein the processing circuitry is configured to: determine anexistence of the flag in the coded video bitstream based on an existingcondition that is modified to base on a comparison of the size and thethreshold.
 15. The apparatus of claim 14, wherein the existing conditiondetermines whether the block is an inter coded block.
 16. The apparatusof claim 14, wherein the existing condition determines whether the IBCmode is enabled.
 17. A non-transitory computer-readable medium storinginstructions which when executed by a computer for video decoding causethe computer to perform: decoding prediction information for a block inan I slice from a coded video bitstream; determining, whether an intrablock copy (IBC) mode is possible for the block in the I slice based onthe prediction information and a size restriction of the IBC mode; inresponse to a slice type parameter indicating the I slice and at least awidth or height of the current block being greater than 64, setting acurrent mode type parameter to MODE_TYPE_INTRA to indicate an intraprediction mode; decoding a flag that indicates whether a skip mode isapplied on the block from the coded video bitstream; and reconstructingthe block at least partially based on the flag.
 18. The non-transitorycomputer-readable medium of claim 17, wherein the instructions cause thecomputer to perform: inferring the flag in response to the IBC modebeing impossible for the block in the I slice.
 19. The non-transitorycomputer-readable medium of claim 17, wherein the instructions cause thecomputer to perform: determining that the IBC mode is impossible for theblock in the I slice in response to a size of the block in the I slicebeing larger than a threshold.
 20. The non-transitory computer-readablemedium of claim 19, wherein the instructions cause the computer toperform: determining that the IBC mode is impossible for the block inthe I slice in response to at least one of a width of the block and aheight of the block being larger than the threshold.